Thunderbird!

K-9 is an open source email client for Android with multi-folder sync, email signatures, Bcc-to-self, return-address configuration, keyboard shortcuts, Exchange Support, message flagging, IMAP deletes, saving attachments, configurable notifications and more.

Microsoft Outlook, part of the Microsoft Office Suite (not to be confused with Microsoft Outlook Express), is a personal information manager that lets you manage your e-mail, calendar, contacts, and tasks.

eM Client is a full featured email client with a modern and easy to use interface. - offers calendar, tasks, contacts and even chat.- fully optimized to run smoothly on Windows XP, Vista, 7, 8 and 10.- supports all major services including Gmail, Exchange, iCloud, and Outlook.com.- easily imports your data from most of the other e-mail clients. This includes Microsoft Outlook, Outlook Express, Windows Mail, Windows Live Mail, Thunderbird, The Bat and more.- fully supports touch devices like touch-enabled laptops, tablets and hybrid devices. Use your email client easily in a modern way.- finds any email, contact or attachment in seconds with eM Client's super-fast search. »

The SeaMonkey project is a community effort to develop the SeaMonkey all-in-one internet application suite. A lighter alternative to Mozilla Firefox. Such a software suite was previously made popular by Netscape and Mozilla, and the SeaMonkey project continues to develop and deliver high-quality updates to this concept. Containing an Internet browser, email and newsgroup client, HTML editor, IRC chat, web development tools, and with plenty of add-ons available, SeaMonkey is sure to appeal to advanced users, web developers and corporate users, as well as to those who need a fast, yet modern, web browser. »

Mailbird is a Windows based email client which design and style match Windows 7, 8 and XP’s native styles. Mailbird provides clean, simple and lightning fast email experience.

Opera Mail powerfully organizes, indexes, and sorts your messages.

Apple Mail changes the way you interact with your email every day.

Geary is a lightweight email program designed around conversations and built for the GNOME desktop.

Postbox is an email application that helps you organize your work life and get stuff done.

Claws Mail is an email client (and news reader), based on GTK+, featuring

Airmail is a lightweight and lightning fast mail client for Mac.

Sylpheed is a simple, lightweight but featureful, and easy-to-use e-mail client (mailer, MUA).